1. Technical Field
The present invention generally relates to an apparatus having an ozonizer, and more particularly to an apparatus for feeding ozone, which is generated by the ozonizer, to a processing unit to use the ozone as an oxidant or the like in the processing unit.
2. Background Art
Conventionally, pulp bleaching is usually carried out using chlorine or oxygen, and in recent years, it is occasionally conducted with ozone.
Use of ozone in pulp bleaching brings about the following advantages: unlike chlorine, it does not require a post-treatment after the bleaching and the bleaching process and/or operation is simpler. Further, better bleaching can be expected than oxygen.
However, a pulp bleaching system which employs ozone has a problem: an initial cost concerning generation of oxygen and ozone is high.
Various types of ozone generator are known in the art. For example, a static discharge type, a ultraviolet type and an electrolysis type are known. Among these, the static discharge type one is the most effective: it can industrially generate the largest amount of ozone. However, a resulting ozone concentration is about 10 vol % at most even if the static discharge type one is employed. Thus, a power efficiency is extremely low, which results in higher running cost.
One conventional ozonizer system is schematically illustrated in FIG. 6 of the accompanying drawings. As shown in FIG. 6, an ozonizer 60 is connected with a reaction vessel 66 in series directly by a feed pipe 63, and ozone O.sub.3 produced in the ozonizer 60 is fed to the reaction vessel 66 together with oxygen O.sub.2. In this system, however, ozone and oxygen exist together so that longevity of ozone is shortened and most of oxygen which is not converted to ozone is expelled to the atmosphere.
To eliminate the above problem, another type of system was developed (Japanese Patent Application, Publication Nos. 52-17385 and 52-35788). One example is schematically illustrated in FIG. 7 of the accompanying drawings. As illustrated, there are provided two absorption towers 62a and 62b which respectively fill up absorbents such as silica gel, and these absorption towers 62a and 62b are situated in parallel downstream of an ozonizer 60. An ozone/oxygen feed line 63 extending from the ozonizer 60 is branched to lines 65a and 65b at a branching point, and the absorption towers 62a and 62b are connected with downstream ends of the branch lines 65a and 65b respectively. The ozonizer 60 generates ozone from oxygen. A changeover valve 64 is provided at the branching point to selectively feed the exhaust gas (i.e., ozone) from the ozonizer 60 into the absorption towers 62a and 62b. Ozone feed pipes 68a and 68b extend from the absorption towers 62a and 62b to a reaction vessel 66. These pipes 68a and 68b meet a point upstream of the reaction vessel 66, at which another valve 69 is provided, so that a single flow of ozone enters the reaction vessel 66 through a pipe 67. Another pair of pipes extend from the absorption towers 62a and 62b to feed back oxygen to the ozonizer 60. These pipes are collected at a confluent point where a third valve 71 is located, and a single pipe 70 returns to the ozonizer 60 from the valve 71.
Upon manipulation of the switching valves 64 and 69, the ozone is introduced to the absorption tower 62a or 62b selectively (or alternatively) from the ozonizer 60 and absorbed and condensed by the absorbent in the absorption tower 62a or 62b selectively (or alternatively). Then, the condensed ozone is released from the absorbent and fed to the reaction vessel 66 from these absorption towers 62a and 62b selectively (or alternatively). Since two absorption towers 62a and 62b are installed, it is possible to continuously feed ozone to the reaction vessel 66. Specifically, alternatively operating the absorption towers 62a and 62b with the valves 64 and 69 results in uninterrupted ozone feeding. And, it is possible to feed ozone only to the reaction vessel 66 while recirculating oxygen to the ozonizer 60 as a raw material gas for the ozonizer 60. In this system, however, a carrier gas for separating or releasing ozone from the absorbent and conveying it to the reaction vessel 66 is necessary, and part of oxygen discharged from the absorption towers 62a and 62b and flowing in the recirculation pipe 70 is used as the carrier gas as indicated by the broken line. As a result, ozone condensed in the absorption towers 62a and 62b is diluted by oxygen before it reaches the reaction vessel 66. If ozone and oxygen exist together, a desired reaction cannot be expected in the reaction vessel 66.
To eliminate this problem, Japanese Patent Application, Laid-Open Publication No. 3-103304 discloses a system which uses an inert gas as a carrier gas. However, this system requires a separate inert gas feeding unit.